1. Field of the Invention
The present invention relates to a metal belt for a continuously variable transmission, comprising a metal ring assembly formed by stacking a plurality of endless metal rings one on another, and a number of metal elements supported on the metal ring assembly, the metal belt being wound around pulleys to transmit a driving force, and in particular, to the metal element which includes a ring slot which is surrounded in three sides by a main body section abutting on V faces of the pulley, a neck section extending to a radial outside from the main body section, and an ear section protruding from a radial outside edge of the neck section to a right and left, the ring slot housing the metal ring assembly therein.
2. Description of the Related Art
Japanese Utility-Model Publication No. 6-6313 has made it known that in a metal belt of a belt type continuously variable transmission, worn-out and fracture of a metal band of the metal belt by contact with a belt engagement section of a metal block is prevented while avoiding abrasion of the metal block by contact with V faces of a pulley, by setting a hardness of the belt engagement section of the metal block, against which a side edge of the metal band abuts, lower than that of the metal band, and by setting a hardness of portions of the metal block other than the above-mentioned belt engagement section higher than that of the V faces of the pulley.
In the meantime, as shown in FIG. 6, in a metal element 32 which includes a ring slot 35 which is surrounded in three sides by a main body section 34 abutting on a V face of a pulley, a neck section 36 extending to a radial outside from the main body section 34, and an ear section 37 protruding from a radial outside edge of the neck section 36 to a right and left, side edges 33a of all the metal rings 33 of a metal ring assembly 31 housed by the ring slot 35 do not contact a metal ring contact surface 36a of the neck section 36 equally. Metal rings 33 in radial inside and radial middle sections where behavior is stable since a lubricant is fully spread hardly contact the metal ring contact surfaces 36a of the neck sections 36, but metal rings 33 in a radial outside where behavior is unstable since a lubricant is not fully spread contact the metal ring contact surfaces 36a of the neck sections 36 frequently.
Nevertheless, the conventional one has a possibility that strength of the metal element may drop sharply and the neck section or the like may break since hardness of a whole region of the metal ring contact surface of the metal block is reduced.